A Sensitive point

A UK-developed system tests the accuracy of a needle used by children to self-administer medication. Dave Wilson reports

When a prominent biotechnology group wanted an automated system to test its new dial-a-dose drug-delivery pen, it turned to Innomech to help with its development.

The pen is used by children to intermittently and regularly self-administer a very high-value active pharmaceutical. In use, the device injects a needle into the skin to deliver a precisely metered amount of a drug, after which the needle is retracted.

The pen has four main active elements: the needle through which the medication is delivered; a spring-loaded contact cup that is pressed against the skin; a rotary dial used to set the required dose and to provide energy to fire an actuator; and the actuation mechanism itself.

Once a user has set the dose through turning the dial and depressed the actuator, the energy stored within an internal spring is released, firing the needle through the contact cup into the skin. The distance the needle travels is relative to the compression cup, so the needle is always moved relative to the skin surface, not the body of the device, to dispense the correct volume of medication to the patient.

Testing such devices is vitally important to ensure they consistently deliver the appropriate dose.

The biotech company had an existing testing procedure that ensured the actuation mechanism functioned correctly and the needle travelled the correct distance with the required force, but this was highly dependent on the skills of an operator.

To advise them on the feasibility of automating the existing quality-control process, while making it more repeatable and accurate, the company approached Cambridgeshire-based Innomech.

Teaming up with the biotech company’s in-house engineers in California, the Innomech engineers conducted an extensive study into the existing and required testing processes, after which they developed a new machine that could deliver a more sophisticated and automated approach.

The device checks 20 parameters in 30 seconds beforeindicating whether the pen has passed or failed

Dr Peter Woods, engineering and programme manager at Innomech, said that in this machine each of the pen’s four mechanisms are performed in concert, reproducing the way it would be used in the field.

At the start of the test, the machine compresses the cup to simulate pressing it against the skin. It then dials a dose by rotating the dial, after which it applies a trigger to the actuator that causes the needle to move with a specific force, which can then be monitored.

’The moving parts under test are each actuated by a servo motor drive that allows them to be moved through a specified profile with great accuracy and repeatability. Load cells measure the force that is applied to each of the parts by the servo drives, which the machine then compares against the profiles of the distances travelled by the moving parts in the pen to determine the performance characteristics of each mechanism,’ explained Dr Woods.

The Innomech engineers realised it was important to be able to demonstrate that measurements made by the machine’s load cells were absolute. Rather than rely on pre-calibrated load cells, they opted to calibrate the machine by using a set of test pieces.

These were designed and manufactured by Innomech then calibrated by the Institute of Spring Technology, an independent test house, which enabled the biotech company to trust in the absolute accuracy of the machine’s measurements and also to trace a single standard through an accredited agency.

Dr Woods said the new machine is extremely simple to operate. An operator simply places a pen inside it, after which the machine pneumatically clamps it into place and in just 30 seconds checks 20 parameters before indicating to the operator whether the pen has passed or failed.

’An operator can visualise whether any of the components that comprise the pen might be drifting out of tolerance, enabling the manufacturer to address component manufacturing issues,’ said Dr Woods.

Production essentials

The key facts to take away from this article:

- Testing the accuracy of a drug-delivery pen is vital in ensuring patient safety - Innomech has developed a testing machine that simulates use in the field - Co-operation with the Institute of Spring Technology has helped ensure absolute accuracy